The present invention generally relates to reticles and methods of making same, and more specifically relates to a method for reducing reticle set cost.
As wafer technologies have become more and more complex, reticle costs have been increasing at a high rate. For example, in G10P (i.e., 0.35 micron node in Tskuba), a full set of reticles for a given device was less than $50,000. In Gflx, the cost of a full set of reticles can exceed $650,000. In G90, the cost for a full set of reticles is expected to be more than $1,500,000.
Many solutions have been attempted to keep reticle costs reasonable. One solution that has been attempted is to place more than one design on a reticle set. A problem is that a multiple chip wafer, which is generated from the multiple chip reticle, is difficult to assemble, saw, and sort (i.e., test). When a wafer is sawed and sorted, one must keep track of which dies are which. While it may be possible to cut each wafer for one type of die, depending on the die size and layout of the die on the wafer, the reticle set cannot be created until all designs are completed, and this may, in turn, delay designs. Additionally, each chip on the wafer may require a different process flow. Assuming there are two designs associated with the reticle set, a common process flow between the two designs must be created. This may be complicated, for example, in the case where one chip is a three layer metal design while the other chip is a four layer metal design. Finally, there is a high probability, depending on die size, that silicon space will be wasted on the wafer. For example, if one die is larger by a non-integer multiplier, generally there is no way to fit the designs on a wafer without leaving open space on the wafer.
Another solution that has been attempted is to use multiple layer reticles. This is a solution that has been used in the industry in connection with Ultratech 1X steppers. The solution involves placing more than one masking layer on each reticle. Individual patterns for each masking layer are given to the mask maker, along with instructions as to where to place the patterns. The mask maker then creates a jobdeck, which places each layer on a given mask in a specified location. The mask maker needs to create the jobdeck correctly, as well as maintain the individual pattern files for each layer. As such, compared to methods used to form standard reticles, this method requires that much more information be transferred to the reticle vendor, and has the potential for having more mistakes.
Still another solution which has been attempted is to reduce reticle specifications and simplify the reticle manufacturing process. The problem with this approach is that reticle specifications can be reduced only to a certain extent. While reducing reticle specifications does generally result in a cost savings, the savings is not enough. While a further approach has been to research the most cost effective methods, including using laser beam systems to generate reticles, the cost of reticles has continued to increase.